This invention relates generally to the fields of polymer chemistry, lithography, and semiconductor fabrication. More specifically, the invention relates to novel alicyclic polymers, particularly substituted norbornene fluoroacrylate copolymers, which are useful in lithographic photoresist compositions, particularly chemical amplification photoresist compositions including ultraviolet, electron-beam, and x-ray photoresists.
There is a desire in the industry for higher circuit density in microelectronic devices made using lithographic techniques. One method of increasing the number of components per chip is to decrease the minimum feature size on the chip, which requires higher lithographic resolution. This has been accomplished over the past twenty years by reducing the wavelength of the imaging radiation from the visible (436 nm) down through the ultraviolet (365 mn) to the deep ultraviolet (DUV) at 248 nm. Development of commercial lithographic processes using ultra-deep ultraviolet radiation, particularly 193 nm, is now becoming of interest. See, for example, Allen et al. (1995), xe2x80x9cResolution and Etch Resistance of a Family of 193 nm Positive Resists,xe2x80x9d J. Photopolym. Sci. and Tech. 8(4):623-636, and Abe et al. (1995), xe2x80x9cStudy of ArF Resist Material in Terms of Transparency and Dry Etch Resistance,xe2x80x9d J. Photopolym. Sci. and Tech. 8(4):637-642. The resists proposed for use with 193 nm imaging radiation do not appear suitable for use with 157 nm radiation due to their poor transparency at the 157 nm wavelength.
Certain attempts have been made to develop 157 nm resists, for example using heavily fluorinated materials such as polytetrafluoroethylene (e.g., Teflon AF(copyright); see Endert et al. (1999) Proc. SPIE-Int. Soc. Opt. Eng, 3618:413-417) or hydridosilsesquioxanes (see U.S. Pat. No. 6,087,064 to Lin et al.). These materials do not, however, have the requisite reactivity or solubility characteristics. The challenge in developing chemically amplified resists for 157 nm lithography is in achieving suitable transparency in polymers that have acid-labile functionalities and developed with industry standard developers in either exposed or unexposed areas depending on whether the resist is positive or negative.
Polymers prepared from trifluoromethyl-substituted acrylates have been described. See, for example, Ito et al. (1981), xe2x80x9cMethyl Alpha-Trifluoromethylacrylate, an E-Beam and UV Resist,xe2x80x9d IBM Technical Disclosure Bulletin 24(4):991, Ito et al. (1982) Macromolecules 15:915-920 which describes preparation of poly(methylxcex1-trifluoromethylacrylate) and poly(xcex1-trifluoromethylacrylonitrile) from their respective monomers, and Ito et al. (1987), xe2x80x9cAnionic Polymerization of xcex1-(Trifluoromethyl)Acrylate,xe2x80x9d in Recent Advances in Anionic Polymerization, T. E. Hogen-Esch and J. Smid, Eds. (Elsevier Science Publishing Co., Inc.), which describes an anionic polymerization method for preparing polymers of trifluoromethylacrylate. Willson et al., Polymer Engineering and Science 23(18):1000-1003, also discuss poly(methyl xcex1-trifluoromethylacrylate) and use thereof in a positive electron beam resist. However, none of these references discloses the utility of trifluoromethyl-substituted acrylate polymers in chemical amplification resists.
Alicyclic polymers have also attracted a great deal of attention for their potential utility in advanced microelectronics technologies. The interest stems from their low dielectric constants and low UV absorption. Polymers of alicyclic monomers such as norbornene are typically prepared by metal-mediated addition or ring-opening metathesis polymerization (ROMP), which suffers from the drawbacks of high cost and possible metal contamination. Alternatively, the electron-rich norbornene monomers can be radically copolymerized with electron-deficient maleic anhydride to produce alternating copolymers, which have been heavily evaluated as 193 nm (ArF excimer laser) resist polymers. The norbornene-maleic anhydride co- and terpolymers can be readily prepared and tend to offer high performance lithographic imaging. However, these polymers tend to exhibit relatively high absorption at 157 nm. Furthermore, the maleic anhydride unit is of low functionality and therefore limits functionalization of such copolymers to only the norbornene monomer unit. It has been difficult to identify electron-deficient monomers that undergo radical copolymerization with norbornene derivatives. Such monomers have now been identified, and this invention now provides novel polymers that are synthesized by radical copolymerization of substituted norbornene derivativesxe2x80x94e.g., hexafluoroisopropanol-substituted norbornenexe2x80x94with comonomers such as xcex1-trifluoromethylacrylic acid and derivatives thereof. The polymers provide a versatile foundation for designing chemical amplification resist systems, particularly deep UV resist systems (e.g., 157 nm, 193 nm and 248 nm resists) that combine high UV transparency, aqueous base development, good dry etch resistance, and chemical amplification imaging capability.
Accordingly, it is a primary object of the invention to address the above-described need in the art by providing novel substituted norbornene fluoroacrylate copolymers suitable for use in lithographic photoresist compositions.
It is another object of the invention to provide a lithographic photoresist composition containing a substituted norbornene fluoroacrylate copolymer.
It is still another object of the invention to provide such a composition wherein the substituted norbornene fluoroacrylate copolymer is transparent to deep ultraviolet radiation, i.e., radiation having a wavelength less than about 250 nm.
It is yet another object of the invention to provide such a composition wherein the substituted norbornene fluoroacrylate copolymer is a copolymer of a norbornene monomer substituted with a fluorine-containing moiety and a fluorinated methacrylic acid, a fluorinated methacrylonitrile or a fluorinated methacrylate.
It is still another object of the invention to provide a method for generating a resist image on a substrate using a photoresist composition as described herein.
It is a further object of the invention to provide a method for forming a patterned structure on a substrate by transferring the aforementioned resist image to the underlying substrate material, e.g., by etching.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one aspect, then, the present invention relates to a substituted norbornene fluoroacrylate copolymer prepared by copolymerization of a first monomer having the structure 
wherein m is zero or 1, r is zero or 1, L is a linking group, R1 is linear or branched fluoroalkyl, R2 is linear or branched alkyl or fluoroalkyl, and R3 is hydrogen, alkyl (preferably lower alkyl), xe2x80x94C(O)R, xe2x80x94CH2xe2x80x94C(O)OR, C(O)OR, or SiR3 wherein R is alkyl, preferably lower alkyl, and at least one additional monomer having the structure (II) 
wherein R4 is xe2x80x94COOH, xe2x80x94CN, an amide, an acid-inert ester, or an acid-cleavable functionality. The polymer may serve as either the base-soluble component of an unexposed resist or as an acid-labile material that releases acid following irradiation.
In another aspect, the invention relates to a lithographic photoresist composition comprising a substituted norbornene fluoroacrylate copolymer as described above and a photosensitive acid generator (also referred to herein as a xe2x80x9cphotoacid generator,xe2x80x9d a xe2x80x9cPAG,xe2x80x9d or a xe2x80x9cradiation-sensitive acid generatorxe2x80x9d).
The present invention also relates to the use of the resist composition in a lithography method. The process involves the steps of (a) coating a substrate (e.g., a ceramic, metal or semiconductor substrate) with a film comprising a radiation-sensitive acid generator and a copolymer as provided herein; (b) exposing the film selectively to a predetermined pattern of radiation to form a latent image therein; and (c) developing the image using a suitable developer composition. The radiation may be ultraviolet, electron beam or x-ray. Ultraviolet radiation is preferred, particularly deep ultraviolet radiation having a wavelength of less than about 250 nm, e.g., 157 nm, 193 nm, or 248 nm. The pattern from the resist structure may then be transferred to the underlying substrate. Typically, the transfer is achieved by reactive ion etching or some other etching technique. Thus, the compositions of the invention and resulting resist structures can be used to create patterned material layer structures such as metal wiring lines, holes for contacts or vias, insulation sections (e.g., damascene trenches or shallow trench isolation), trenches for capacitor structures, etc. as might be used in the design of integrated circuit devices.
Before describing the present invention in detail, it is to be understood that this invention is not limited to specific compositions, components or process steps, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
It must be noted that, as used in this specification and the appended claims, the singular forms xe2x80x9ca,xe2x80x9d xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to xe2x80x9ca monomerxe2x80x9d includes a combination of two or more monomers that may or may not be the same, a xe2x80x9cphotoacid generatorxe2x80x9d includes a mixture of two or more photoacid generators, and the like.
In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.
The term xe2x80x9calkylxe2x80x9d as used herein refers to a branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, decyl, tetradecyl, hexadecyl, eicosyl, tetracosyl and the like, as well as cycloalkyl groups such as cyclopentyl, cyclohexyl and the like. The term xe2x80x9clower alkylxe2x80x9d intends an alkyl group of 1 to 6 carbon atoms, and the term xe2x80x9clower alkyl esterxe2x80x9d refers to an ester functionality xe2x80x94C(O)Oxe2x80x94R wherein R is lower alkyl.
The term xe2x80x9calkylenexe2x80x9d as used herein refers to a difunctional branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms, such as methylene, ethylene, n-propylene, n-butylene, n-hexylene, decylene, tetradecylene, hexadecylene, and the like. The term xe2x80x9clower alkylenexe2x80x9d refers to an alkylene group of one to six carbon atoms.
The term xe2x80x9cfluorinatedxe2x80x9d refers to replacement of a hydrogen atom in a molecule or molecular segment with a fluorine atom. The term xe2x80x9cperfluorinatedxe2x80x9d is also used in its conventional sense to refer to a molecule or molecular segment wherein all hydrogen atoms are replaced with fluorine atoms. Thus, a xe2x80x9cfluorinatedxe2x80x9d methyl group encompasses xe2x80x94CH2F and xe2x80x94CHF2 as well as the xe2x80x9cperfluorinatedxe2x80x9d methyl group xe2x80x94CF3.
xe2x80x9cOptionalxe2x80x9d or xe2x80x9coptionallyxe2x80x9d means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. For example, the phrase xe2x80x9coptionally substituted lower alkylxe2x80x9d means that a lower alkyl moiety may or may not be substituted and that the description includes both unsubstituted lower alkyl and lower alkyl where there is substitution.
The term xe2x80x9cpolymerxe2x80x9d is used to refer to a chemical compound that comprises linked monomers, and that may be linear, branched, or crosslinked.
The terms xe2x80x9cphotogenerated acidxe2x80x9d and xe2x80x9cphotoacidxe2x80x9d are used interchangeably herein to refer to the acid that is created upon exposure of the present compositions to radiation, i.e., as a result of the radiation-sensitive acid generator in the compositions.
The term xe2x80x9csubstantially transparentxe2x80x9d as used to describe a polymer that is xe2x80x9csubstantially transparentxe2x80x9d to radiation of a particular wavelength refers to a polymer that has an absorbance of less than about 5.0/micron, preferably less than about 4.0/micron, most preferably less than about 3.5/micron, at a selected wavelength.
For additional information concerning terms used in the field of lithography and lithographic compositions, reference may be had to Introduction to Microlithography, Eds. Thompson et al. (Washington, D.C.: American Chemical Society, 1994).
The fluorinated norbornene copolymer is prepared by copolymerization of a monomer having the structure (I) 
wherein m is zero or 1, r is zero or 1, L is an alkylene or oxyalkylene linking group, R1 is linear or branched fluoroalkyl, R2 is linear or branched alkyl or fluoroalkyl, and R3 is hydrogen, alkyl (preferably lower alkyl), xe2x80x94C(O)xe2x80x94R, xe2x80x94CH2xe2x80x94C(O)OR, xe2x80x94C(O)OR or Si(R)3 wherein R is alkyl, preferably lower alkyl (e.g., R3 may be xe2x80x94C(O)OC(CH3)3, xe2x80x94CH2C(O)OC(CH3)3, xe2x80x94C(O)CH3, or xe2x80x94Si(CH3)3), and at least one additional monomer having the structure (II) 
wherein R4 is xe2x80x94COOH, xe2x80x94CN, an amide, an acid-inert moiety such as an acid-inert ester, or an acid-cleavable functionality. The polymer may serve as either the base-soluble component of an unexposed resist or as an acid-labile material that releases acid.
The aforementioned copolymer will thus comprise monomer units having the structure of formula (III) 
wherein m, r, L, R1, R2 and R3 are as defined above, and at least one additional monomer unit having the structure (IV) 
In the second monomer, R4 is xe2x80x94COOH, xe2x80x94CN, an amide, an acid-inert moiety such as an acid-inert ester, or an acid-cleavable functionality, i.e., a molecular moiety that is cleavable with acid, particularly photogenerated acid. Suitable acid-cleavable functionalities include, but are not limited to, esters, carbonates, ketals and acetals, exemplified below: 
wherein m is in the range of 1 to 3, n is zero or 1, R6 is hydrogen, lower alkyl (e.g., methyl, ethyl, isopropyl, etc.), fluorinated lower alkyl (e.g., trifluoromethyl, pentafluoroethyl, 1,1,1,3,3,3-hexafluoroisopropyl), or lower alkyl substituted with a tri(lower alkyl)silyl group (e.g., trimethylsilyl-substituted ethyl, or xe2x80x94CH2CH2Si(CH3)3), or is selected so as to provide an acid-cleavable substituent, R7 and R8 are lower alkyl or are linked to form a five-or six-membered heterocyclic ring that may or may not contain an additional heteroatom and/or a carbonyl moiety, R9 and R10 are hydrogen, lower alkyl, or fluorinated lower alkyl, n is zero or 1, and L is a linking group, and R11 is lower alkyl, fluorinated lower alkyl, or lower alkyl substituted with a tri(lower alkyl)silyl group, or is selected so as to provide an acid-cleavable substituent. Preferably, R4 has the structure of formula (V), and R6 is selected so as to provide an acid-cleavable functionality, i.e., a molecular moiety that is cleavable with acid, particularly photogenerated acid.
Preferred acid-cleavable pendant groups are organic ester groups that undergo a cleavage reaction in the presence of photogenerated acid to generate a carboxylic acid group. Typically, the reaction of acid-cleavable functional groups with photogenerated acid occurs only, or is promoted greatly by, the application of heat to the film. Those skilled in the art will recognize the various factors that influence the rate and ultimate degree of cleavage of acid-cleavable functional groups as well as the issues surrounding integration of the cleavage step into a viable manufacturing process. The product of the cleavage reaction is a polymer-bound acid group, which, when present in sufficient quantities along the polymer backbone, imparts solubility to the polymer in basic aqueous solutions.
The copolymer may comprise different monomer units each having the structure (III), different monomer units each having the structure (IV) and/or one or more other monomer units, typically formed from addition polymerizable monomers, preferably vinyl monomers, for example to enhance the performance of the photoresist. Thus, the polymer may comprise minor amounts of acrylic acid or methacrylic acid monomer (e.g., 5-30%) to enhance development. The polymer may also comprise other suitable monomer units such as hydroxystyrene to enhance development and etch resistance or a silicon-containing monomer unit (e.g., a silicon-containing acrylate, methacrylate or styrene) to enhance oxygen plasma etch resistance for bilayer applications. In general, suitable comonomers include, but are not limited to, the following ethylenically unsaturated polymerizable monomers: acrylic and methacrylic acid esters and amides, including alkyl acrylates, aryl acrylates, alkyl methacrylates and aryl methacrylates (for example, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, benzyl acrylate and N-phenylacrylamide); vinyl aromatics, including unsubstituted styrene and styrene substituted with one or two lower alkyl, halogen or hydroxyl groups (for example, styrene derivatives such as 4-vinyltoluene, 4-vinylphenol, xcex1-methylstyrene, 2,5-dimethylstyrene, 4-t-butylstyrene and 2-chlorostyrene); butadiene; vinyl acetate; vinyl bromide; vinylidene chloride; and C5-C20, generally C7-C15, cyclic olefin monomers such as norbornene and tetracyclododecane; fluorinated analogs of any of the foregoing, e.g., fluorinated acrylic and methacrylic acid esters (e.g., fluorinated alkyl acrylates, fluorinated aryl acrylates, fluorinated alkyl methacrylates and fluorinated aryl methacrylates); and others readily apparent to one skilled in the art. The structure (III) and structure (IV) monomer units will generally be present in a ratio of approximately 1:2; that is, the copolymer will generally comprise approximately 30-40% structure (III) monomer units and, correspondingly, approximately 70%-60% structure (IV) monomer units. This is not necessarily the case, however, if additional types of monomer units are present.
The present copolymers may be readily synthesized using methods described in the pertinent texts and literature, or as known to those of ordinary skill in the art. Methods for synthesizing representative monomers are described in the examples, as are methods for preparing the fluorinated norbornene copolymers.
The copolymers of the invention can be prepared by radical copolymerization, using a suitable free radical initiator. The initiator may be any conventional free radical-generating polymerization initiator. Examples of suitable initiators include peroxides such as O-t-amyl-O-(2ethylhexyl)monoperoxycarbonate, dipropylperoxydicarbonate, and benzoyl peroxide (BPO) as well as azo compounds such as azobisisobutyronitrile (AIBN), 2,2xe2x80x2-azobis(2-amidino-propane)dihydrochloride, and 2,2xe2x80x2-azobis(isobutyramide)dihydrate. The initiator is generally present in the polymerization mixture in an amount of from about 0.2 to 5% by weight of the monomers. The resulting copolymer typically as a number average molecular weight in the range of approximately 500 to 50,000, generally in the range of approximately 1,000 to 15,000.
The second component of the resist composition is a photoacid generator. Upon exposure to radiation, the photoacid generator generates a strong acid. A variety of photoacid generators can be used in the composition of the present invention. The photosensitive acid generators used in the photoresist compositions of the invention may be any suitable photosensitive acid generator known in the art which is compatible with the other components of the photoresist composition. Examples of preferred photoresist acid generators (PAGs) include, but are not limited to, xcex1-(trifluoromethylsulfonyloxy)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide (MDT), onium salts, aromatic diazonium salts, sulfonium salts, diaryliodonium salts and sulfonic acid esters of N-hydroxyamides or -imides, as disclosed in U.S. Pat. No. 4,731,605. Also, a PAG that produces a weaker acid such as dodecane sulfonate of N-hydroxy-naphthalimide (DDSN) may be used. Combinations of PAGs may be used. Generally, suitable acid generators have a high thermal stability (preferably to temperatures greater than 140xc2x0 C.) so they are not degraded during pre-exposure processing. In addition to MDT and DDSN, suitable sulfonate compounds are sulfonate salts, but other suitable sulfonate PAGs include sulfonated esters and sulfonyloxy ketones. See U.S. Pat. No. 5,344,742 to Sinta et al., and J. Photopolymer Science and Technology, 4:337-340 (1991), for disclosure of suitable sulfonate PAGs, including benzoin tosylate, t-butylphenyl xcex1-(p-toluenesulfonyloxy)-acetate and t-butyl xcex1-(p-toluenesulfonyloxy)-acetate. Onium salts are also generally preferred acid generators of compositions of the invention. Onium salts that contain weakly nucleophilic anions have been found to be particularly suitable. Examples of such anions are the halogen complex anions of divalent to heptavalent metals or non-metals, for example, Sb, B, P, and As. Examples of suitable onium salts are aryl-diazonium salts, halonium salts, aromatic sulfonium salts and sulfoxonium salts or selenium salts, (e.g., triarylsulfonium and diaryliodonium hexafluoroantimonates, hexafluoroarsenates, trifluoromethanesulfonates and others). Examples of suitable preferred onium salts can be found in U.S. Pat. Nos. 4,442,197, 4,603,101, and 4,624,912. Other useful acid generators include the family of nitrobenzyl esters, and the s-triazine derivatives. Suitable s-triazine acid generators are disclosed, for example, in U.S. Pat. No. 4,189,323.
Still other suitable acid generators include N-camphorsulfonyloxynaphthalimide, N-pentafluorophenylsulfonyloxynaphthalimide, ionic iodonium sulfonates, e.g., diaryl iodonium (alkyl or aryl) sulfonate and bis-(di-t-butylphenyl)iodonium camphanylsulfonate, perfluoroalkanesulfonates, such as perfluoropentanesulfonate, perfluoromethanesulfonate; aryl (e.g., phenyl or benzyl) triflates and derivatives and analogs thereof, e.g., triphenylsulfonium triflate or bis-(t-butylphenyl)iodonium triflate; pyrogallol derivatives (e.g., trimesylate of pyrogallol); trifluoromethanesulfonate esters of hydroxyimides, xcex1,xcex1xe2x80x2-bis-sulfonyl-diazomethanes; sulfonate esters of nitro-substituted benzyl alcohols; naphthoquinone-4-diazides; and alkyl disulfones. Other suitable photoacid generators are disclosed in Reichmanis et al. (1991), Chemistry of Materials 3:395, and in U.S. Pat. No. 5,679,495 to Yamachika et al. Additional suitable acid generators useful in conjunction with the compositions and methods of the invention will be known to those skilled in the art and/or are described in the pertinent literature.
The photoresist composition herein comprises both a fluorinated norbornene copolymer as described in detail above and an acid generator, with the polymer representing up to about 99 wt. % of the solids included in the composition, and the photoacid generator representing approximately 0.5-10 wt. % of the solids contained in the composition. Other components and additives may also be present.
For example, a positive photoresist composition may include a dissolution inhibitor, and a negative photoresist composition will include a crosslinking agent. If dissolution inhibitors and crosslinking agents are present, they will typically represent in the range of about 1 wt. % to 40 wt. %, preferably about 5 wt. % to 30 wt. %, of the total solids.
Suitable dissolution inhibitors will be known to those skilled in the art and/or described in the pertinent literature. Preferred dissolution inhibitors have high solubility in the resist composition and the solvent used to prepare solutions of the resist composition (e.g., propylene glycol methyl ether acetate, or xe2x80x9cPGMEAxe2x80x9d), exhibit strong dissolution inhibition, have a high exposed dissolution rate, are substantially transparent at the wavelength of interest, exhibit a moderating influence on Tg, strong etch resistance, and display good thermal stability (i.e., stability at temperatures of about 140xc2x0 C. or greater). Suitable dissolution inhibitors include, but are not limited to, bisphenol A derivatives and carbonate derivatives, for example bisphenol A derivatives wherein one or both hydroxyl moieties are converted to a t-butoxy substituent or a derivative thereof such as a t-butoxycarbonyl or t-butoxycarbonylmethyl group; fluorinated bisphenol A derivatives such as CF3-bisphenol Axe2x80x94OCH2(CO)xe2x80x94O-tBu (6F-bisphenol A protected with a t-butoxycarbonylmethyl group); normal or branched chain acetal groups such as 1-ethoxyethyl, 1-propoxyethyl, 1-n-butoxyethyl, 1-isobutoxy-ethyl, 1-t-butyloxyethyl, and 1-t-amyloxyethyl groups; and cyclic acetal groups such as tetrahydrofuranyl, tetrahydropyranyl, and 2-methoxytetrahydropyranyl groups; androstane-17-alkylcarboxylates and analogs thereof, wherein the 17-alkylcarboxylate at the 17-position is typically lower alkyl. Examples of such compounds include lower alkyl esters of cholic, ursocholic and lithocholic acid, including methyl cholate, methyl lithocholate, methyl ursocholate, t-butyl cholate, t-butyl lithocholate, t-butyl ursocholate, and the like (see, e.g., Allen et al. (1995) J. Photopolym. Sci. Technol., cited supra); hydroxyl-substituted analogs of such compounds (ibid.); and androstane-17-alkylcarboxylates substituted with 1 to 3 C1-C4 fluoroalkyl carbonyloxy substituents, such as t-butyl trifluoroacetyllithocholate (see, e.g., U.S. Pat. No. 5,580,694 to Allen et al.).
The crosslinking agent used in the photoresist compositions of the invention may be any suitable crosslinking agent known in the negative photoresist art which is otherwise compatible with the other selected components of the photoresist composition. The crosslinking agents preferably act to crosslink the polymer component in the presence of a generated acid. Preferred crosslinking agents are glycoluril compounds such as tetramethoxymethyl glycoluril, methylpropyltetramethoxymethyl glycoluril, and methylphenyltetramethoxymethyl glycoluril, available under the POWDERLINK trademark from American Cyanamid Company. Other possible crosslinking agents include: 2,6-bis(hydroxymethyl)-p-cresol and compounds having the following structures: 
including their analogs and derivatives, such as those found in Japanese Laid-Open Patent Application (Kokai) No. 1-293339, as well as etherified amino resins, for example methylated or butylated melamine resins (N-methoxymethyl- or N-butoxymethyl-melamine respectively) or methylated/butylated glycolurils, for example as can be found in Canadian Patent No. 1 204 547. Combinations of crosslinking agents may be used.
The remainder of the resist composition is composed of a solvent and may additionally, if necessary or desirable, include customary additives such as dyes, sensitizers, additives used as stabilizers and acid-diffusion controlling agents, coating aids such as surfactants or anti-foaming agents, adhesion promoters and plasticizers.
The choice of solvent is governed by many factors not limited to the solubility and miscibility of resist components, the coating process, and safety and environmental regulations. Additionally, inertness to other resist components is desirable. It is also desirable that the solvent possess the appropriate volatility to allow uniform coating of films yet also allow significant reduction or complete removal of residual solvent during the post-application bake process. See, e.g., Introduction to Microlithography, Eds. Thompson et al., cited previously. In addition to the above components, the photoresist compositions of the invention generally include a casting solvent to dissolve the other components so that the overall composition may be applied evenly on the substrate surface to provide a defect-free coating. Where the photoresist composition is used in a multilayer imaging process, the solvent used in the imaging layer photoresist is preferably not a solvent to the underlayer materials, otherwise the unwanted intermixing may occur. Examples of suitable casting solvents include: ethoxyethylpropionate (xe2x80x9cEEPxe2x80x9d), a combination of EEP and xcex3-butyrolactone (xe2x80x9cGBLxe2x80x9d), PGMEA, and ethyl lactate. The invention is not limited to selection of any particular solvent. Solvents may generally be chosen from ether, ester-, hydroxyl-, and ketone-containing compounds, or mixtures of these compounds. Examples of appropriate solvents include cyclopentanone, cyclohexane, lactate esters such as ethyl lactate, alkylene glycol alkyl ether esters such as propylene glycol methyl ether acetate, alkylene glycol monoalkyl eters such as methyl cellosolve, butyl acetate, 2-ethoxyethanol, and ethyl 3-ethoxypropionate. Preferred solvents include ethyl lactate, propylene glycol methyl ether acetate, ethyl 3-ethoxypropionate and their mixtures. The above list of solvents is for illustrative purposes only and should not be viewed as being comprehensive nor should the choice of solvent be viewed as limiting the invention in any way. Those skilled in the art will recognize that any number of solvents or solvent mixtures may be used.
Greater than 50 percent of the total mass of the resist formulation is typically composed of the solvent, preferably greater than 80 percent.
Other customary additives include dyes that may be used to adjust the optical density of the formulated resist and sensitizers which enhance the activity of photoacid generators by to absorbing radiation and transferring it to the photoacid generator. Examples include aromatics such as functionalized benzenes, pyridines, pyrimidines, biphenylenes, indenes, naphthalenes, anthracenes, coumarins, anthraquinones, other aromatic ketones, and derivatives and analogs of any of the foregoing.
A wide variety of compounds with varying basicity may be used as stabilizers and acid-diffusion controlling additives. They may include nitrogenous compounds such as aliphatic primary, secondary, and tertiary amines, cyclic amines such as piperidines, pyrimidines, morpholines, aromatic heterocycles such as pyridines, pyrimidines, purines, imines such as diazabicycloundecene, guanidines, imides, amides, and others. Ammonium salts may also be used, including ammonium, primary, secondary, tertiary, and quaternary alkyl- and arylammnonium salts of alkoxides including hydroxide, phenolates, carboxylates, aryl and alkyl sulfonates, sulfonamides, and others. Other cationic nitrogenous compounds including pyridinium salts and salts of other heterocyclic nitrogenous compounds with anions such as alkoxides including hydroxide, phenolates, carboxylates, aryl and alkyl sulfonates, sulfonamides, and the like may also be employed. Surfactants may be used to improve coating uniformity, and include a wide variety of ionic and non-ionic, monomeric, oligomeric, and polymeric species. Likewise, a wide variety of anti-foaming agents may be employed to suppress coating defects. Adhesion promoters may be used as well; again, a wide variety of compounds may be employed to serve this function. A wide variety of monomeric, oligomeric, and polymeric plasticizers such as oligo- and polyethyleneglycol ethers, cycloaliphatic esters, and non-acid reactive steroidally-derived materials may be used as plasticizers, if desired. However, neither the classes of compounds nor the specific compounds mentioned above, are intended to be comprehensive and/or limiting. One versed in the art will recognize the wide spectrum of commercially available products that may be used to carry out the types of functions that these customary additives perform.
Typically, the sum of all customary additives will comprise less than 20 percent of the solids included in the resist formulation, preferably, less than 5 percent.
The present invention also relates to a process for generating a resist image on a substrate comprising the steps of: (a) coating a substrate with a film comprising the resist composition of the present invention; (b) imagewise exposing the film to radiation; and (c) developing the image. The first step involves coating the substrate with a film comprising the resist composition dissolved in a suitable solvent. Suitable substrates are ceramic, metallic or semiconductive, and preferred substrates are silicon-containing, including, for example, silicon dioxide, silicon nitride, and silicon oxynitride. The substrate may or may not be coated with an organic anti-reflective layer prior to deposition of the resist composition. Alternatively, a bilayer resist may be employed wherein a resist composition of the invention forms an upper resist layer (i.e., the imaging layer), and the underlayer is comprised of a material that is highly absorbing at the imaging wavelength and compatible with the imaging layer. Conventional underlayers include diazonapthoquinone (DNQ)/novolak resist material.
Preferably, the surface of the substrate is cleaned by standard procedures before the film is deposited thereon. Suitable solvents for the composition are as described in the preceding section, and include, for example, cyclohexanone, ethyl lactate, and propylene glycol methyl ether acetate. The film can be coated on the substrate using art-known techniques such as spin or spray coating, or doctor blading. Preferably, before the film has been exposed to radiation, the film is heated to an elevated temperature of about 90-150xc2x0 C. for a short period of time, typically on the order of about 1 minute. The dried film has a thickness of about 0.02-5.0 microns, preferably about 0.05-2.5 microns, most preferably about 0.10 to 1.0 microns. The radiation may be ultraviolet, electron beam or x-ray. Ultraviolet radiation is preferred, particularly deep ultraviolet radiation having a wavelength of less than about 250 nm, e.g., 157 nm using an F2 excimer laser. The radiation is absorbed by the radiation-sensitive acid generator to generate free acid which with heating causes cleavage of the acid-cleavable pendant groups and formation of the corresponding acid. After the film has been exposed to radiation, the film may again be heated to an elevated temperature of about 90-150xc2x0 C. for a short period of time, on the order of about 1 minute. It will be appreciated by those skilled in the art that the aforementioned description applies to a positive resist, and with a negative resist the exposed regions would typically be crosslinked by acid.
The third step involves development of the image with a suitable solvent. Suitable solvents include an aqueous base, preferably an aqueous base without metal ions such as the industry standard developer tetramethylammonium hydroxide or choline. Because the fluorinated norbornene copolymer of the resist composition is substantially transparent at 157 nm, the resist composition is uniquely suitable for use at that wavelength. However, the resist may also be used with wavelengths of 193 nm and 248 nm, or with electron beam or x-ray radiation.
The pattern from the resist structure may then be transferred to the material of the underlying substrate. Typically, the transfer is achieved by reactive ion etching or some other etching technique. Thus, the compositions of the invention and resulting resist structures can be used to create patterned material layer structures such as metal wiring lines, holes for contacts or vias, insulation sections (e.g., damascene trenches or shallow trench isolation), trenches for capacitor structures, etc. as might be used in the design of integrated circuit devices. Accordingly, the processes for making these features involves, after development with a suitable developer as above, etching the layer(s) underlying the resist layer at spaces in the pattern whereby a patterned material layer or substrate section is formed, and removing any remaining resist from the substrate. In some instances, a hard mask may be used below the resist layer to facilitate transfer of the pattern to a further underlying material layer or section. In the manufacture of integrated circuits, circuit patterns can be formed in the exposed areas after resist development by coating the substrate with a conductive material, e.g., a metallic material, using known techniques such as evaporation, sputtering, plating, chemical vapor deposition, or laser-induced deposition. Dielectric materials may also be deposited by similar means during the process of making circuits. Inorganic ions such as boron, phosphorous, or arsenic can be implanted in the substrate in the process for making p-doped or n-doped circuit transistors. Examples of such processes are disclosed in U.S. Pat. Nos. 4,855,017, 5,362,663, 5,429,710, 5,562,801, 5,618,751, 5,744,376, 5,801,094, and 5,821,469. Other examples of pattern transfer processes are described in Chapters 12 and 13 of Moreau, Semiconductor Lithography, Principles, Practices, and Materials (Plenum Press, 1988). It should be understood that the invention is not limited to any specific lithographic technique or device structure.
It is to be understood that while the invention has been described in conjunction with the preferred specific embodiments thereof, that the foregoing description as well as the examples which follow are intended to illustrate and not limit the scope of the invention. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.
All patents, patent applications, and publications mentioned herein are hereby incorporated by reference in their entirety.